An MS relapse is also known as a flare-up, exacerbation, or attack. For a true relapse or flare-up, worsened symptoms need to last at least 24 hours and occur at least 30 days after a previous relapse.

Multiple sclerosis (MS) is a chronic neurological condition that causes problems with your central nervous system (CNS). With this autoimmune disorder, your immune system mistakenly attacks myelin throughout the CNS, leading to scar tissue or plaques. Myelin is the protective sheath around nerve cells.

While everyone with MS experiences this condition differently, it’s commonly known for causing periods of relapses and remission. As MS progresses, there may be fewer times of remission, with symptoms becoming steadier.

People often use the terms “flare-up” and “relapse” interchangeably when talking about MS, though you’re more likely to hear the latter. Aside from key terminology, here’s the important information you need to know about MS relapses.

An MS flare-up is a period when your symptoms are worse than usual because of increased CNS inflammation. Flare-ups also occur in other autoimmune diseases, such as lupus, rheumatoid arthritis (RA), and inflammatory bowel disease (IBD).

In MS, a flare-up is also called a relapse. Other common names for a relapse include exacerbation or attack. For symptoms to constitute a true flare-up or relapse, they must occur for 24 hours or longer and develop 30 days or longer after a previous relapse.

During an MS relapse, you may experience new neurological symptoms or existing symptoms that increase in severity or flare up. The term “relapse” is most often used in this condition because of its varying periods of remission and exacerbations.

Symptoms of an MS flare-up

Some of the most common symptoms seen during an MS relapse or flare-up include:

  • fatigue
  • vision problems
  • cognitive difficulties
  • numbness
  • stiffness
  • spasticity
  • difficulty with balance and walking
  • bladder and bowel problems
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Sometimes, symptoms similar to an MS relapse may occur due to worsening of preexisting symptoms. This is known as a pseudo-relapse. It’s not due to any new inflammation or active disease. Stress, heat, or an infection can trigger a pseudo-relapse.

Pseudo-relapses do not require treatment with corticosteroids. An MRI can help doctors distinguish between a pseudo-relapse and a true relapse.

Relapsing-remitting MS (RRMS) is the most common of the four main types of MS. It’s characterized by recurring acute relapses, commonly called “attacks.” According to the National MS Society, about 85% of new MS diagnoses are initially RRMS.

During an RRMS relapse, your symptoms may worsen before you experience remission. Depending on your MS severity, you may still have symptoms of MS during remission, but these aren’t as severe as they are during a relapse.

The time between a relapse and remission from RRMS varies. Some people may experience remission for several weeks or months at a time, while others in earlier stages of MS might experience remission for many years.

On average, people with RRMS have this condition for about 10 years before it progresses to secondary-progressive MS (SPMS). With progressive forms of MS, you may experience symptoms, but they’re more stable and less likely to flare up acutely, as in RRMS.

You may be experiencing an MS relapse if you have new or worsening symptoms that last for 24 hours or more. If symptoms are within 30 days of a previous MS relapse, healthcare professionals consider them part of the previous relapse.

Relapse symptoms are also separate from an active infection.

Symptoms of an MS relapse are also variable, ranging from mild to severe. In some cases, you might experience mild discomfort that doesn’t stop you from participating in everyday activities. In more severe instances, MS may significantly disrupt your daily life.

While not all MS flare-ups require medical attention, contacting a doctor is important if you’re experiencing any new symptoms. In particular, a medical professional can assess any new changes in vision or balance.

You can also consider seeing a doctor if you’re experiencing signs of a severe relapse. In such cases, a doctor may prescribe a high dose corticosteroid on a short-term basis to treat the underlying acute inflammation.

Consider discussing the following frequently asked questions about MS relapses with a doctor.

How long is the average MS flare-up?

There’s no set timeline for an MS relapse, and each flare-up may be different from the last. On average, symptoms of an MS flare-up may last several days, weeks, or months at a time.

What triggers an MS flare-up?

Factors like low vitamin D levels, male sex, younger age, and genetics may increase your risk of a relapse over time. Other factors, like infection, stress, recent childbirth, and withdrawal from a disease-modifying medication, can trigger an acute relapse.

Can you go years without an MS relapse?

It’s possible to go several years without experiencing an MS relapse. This is especially true if you have RRMS. With progressive forms of MS, such as secondary- and primary-progressive MS, you may experience steady symptoms with few or no noticeable relapses.

Can you have MS and no relapses?

Primary-progressive MS (PPMS) is one type of MS that medical professionals characterize by a steady progression of symptoms and no relapses. However, the symptoms gradually worsen over time. This is also a less common form of MS.

An MS flare-up is commonly called a relapse. Healthcare professionals also refer to it as an attack or exacerbation.

Regardless of the name, having a flare-up or relapse means you’ve experienced new or worsening MS symptoms for longer than a full day. This is due to underlying inflammation of your CNS and may last for several days or longer.

If you have any concerns about an MS relapse, including any new or particularly severe symptoms, see a doctor for help.